Showing papers on "Light scattering published in 1986"
Book•
03 Jul 1986
TL;DR: Degenerate four-wave mixing (DFWM) as mentioned in this paper is a simple method to achieve phase conjugation, i.e. to generate a wave which propagates time reversed with respect to an incident wave.
Abstract: The invention ofthe laser 25years ago resulted in powerfullight sources which led to the observation of unexpected and striking phenomena. New fields of science such as holography and nonlinear optics developed constituting the basis of this volume. The classical principle of linear superposition of light wavesdoes not hold anymore. Two laser beams crossing in a suitable material may produce a set of new beams with different directions and frequencies. The interaction of light waves can be understood by considering the optical grating structures which develop in the overlap region. The optical properties of matter become spatially modulated in the interference region of two light waves. Permanent holographic gratings have been produced in this way by photographic processes for many years. In contrast, dynamic or transient gratings disappear after the inducing light source, usually a laser, has been switched off. The grating amplitude is controlled by the light intensity. Dynamic gratings have been induced in a large number ofsolids, liquids, and gases, and are detected by diffraction, 'forced light scattering' of a third probing beam, or by self-diffraction of the light waves inducing the grating. The combined interference and diffraction effect corresponds to four-wave mixing (FWM) in the language of nonlinear optics. The process is called degenerate ifthe frequenciesofthe three incident wavesand the scattered wave are equal. Degenerate four-wave mixing (DFWM) is a simple method to achieve phase conjugation, i.e. to generate a wave which propagates time reversed with respect to an incident wave.
1,054 citations
TL;DR: In this article, the light scattering and electro-optic response of new material with display potential are investigated, which consist of microdroplets of nematic liquid crystals which are spontaneously formed in a solid polymer at the time of its polymerization.
Abstract: The light scattering and electro‐optic response of new material with display potential are investigated. The materials consist of microdroplets of nematic liquid crystals which are spontaneously formed in a solid polymer at the time of its polymerization. Droplet size, spacing, and distribution are readily controlled in these materials to allow optimization of displays based upon electrically controlled light scattering from the liquid crystal droplets. Preliminary experimental and theoretical studies of the light scattering properties show these materials to offer new features suitable for many display applications.
1,044 citations
TL;DR: In this paper, an analytical model was developed for the opposition effect (heiligenshein) in the case of light scattering from a semi-infinite, particulate medium with particles that are large relative to the wavelength.
662 citations
TL;DR: In this article, Raman intensity data were obtained from liquid water between 3.5 and 89.3°C using holographic grating double and triple monochromators.
Abstract: Low frequency Δν=0–350 cm−1, Raman intensity data were obtained from liquid water between 3.5 and 89.3 °C using holographic grating double and triple monochromators. The spectra were Bose–Einstein (BE) corrected, I/(1+n), and the total integrated (absolute) contour intensities were treated by an elaboration of the Young–Westerdahl (YW) thermodynamic method, assuming conservation of hydrogen‐bonded (HB) and nonhydrogen‐bonded (NHB=bent and/or stretched, O–H O) nearest‐neighbor O–O pairs. A ΔH°1 value of 2.6±0.1 kcal/mol O–H ⋅⋅⋅ O or 5.2±0.2 kcal/mol H2O (11 kJ/mol O–H ⋅⋅⋅ O, or 22 kJ/mol H2O) resulted for the HB→NHB process. This intermolecular value agrees quantitatively with Raman and infrared ΔH° values from the one‐ and two‐phonon OH‐stretching regions, and from molecular dynamics, depolarized light scattering, neutron scattering, and ultrasonic absorption, thus indicating a common process. A population involving partial covalency of, i.e., charge transfer into, the H ⋅⋅⋅ O units of linear and/or weak...
550 citations
TL;DR: The experimental line shape of the albedo within the diffusion approximation is analyzed and explained to explain the observed effects of polarization.
Abstract: Recent experiments have confirmed that coherent effects in the multiple scattering of light affect the angular dependence of the intensity reflected by disordered media. By considering the constructive interferences between time-reversed paths of light in a semi-infinite medium, we analyze the experimental line shape of the albedo within the diffusion approximation and explain the observed effects of polarization.
497 citations
TL;DR: In this article, the main part of laser investigations concerns with nonlinear optical phenomena, and the knowledge of laws governing the interaction of a powerful light with a medium is necessary for the correct utilization of laser beams.
Abstract: As a result of development of optics during many centuries the concept was formed that a medium can strongly influence on the light propagation, but the light itself cannot have backward influence on the medium. That concept was refuted only with appearing of coherent and high power radiation of lasers, see, e.g., Nobel Lecture by N. Bloembergen in 1981. A new field in physics–nonlinear optics—formed as a result. The main part of laser investigations concerns with nonlinear optical phenomena, nowadays. First of all these phenomena are of extraordinary interest and beauty and provide for new methods of physical investigations. Secondly, the knowledge of laws governing the interaction of a powerful light with a medium is necessary for the correct utilization of laser beams. Finally, a great number of devices of up-to-date laser optics is totally based on utilization of nonlinear optical effects; generation of higher harmonics of light, stimulated scattering of light, optical phase conjugation, self...
394 citations
01 Dec 1986
TL;DR: In this article, it was shown that it is possible to measure the complete scattering matrix of an object using data acquired on a single aircraft pass, and can combine the signals later in the data processor to generate radar images corresponding to any desired combination of transmit and receive polarization.
Abstract: It was shown that it is possible to measure the complete scattering matrix of an object using data acquired on a single aircraft pass, and can combine the signals later in the data processor to generate radar images corresponding to any desired combination of transmit and receive polarization. Various scattering models predict different dependence on polarization state of received power from an object. The imaging polarimeter permits determination of this dependence, which is called the polarization signature, of each point in a radar image. Comparison of the theoretical predictions and observational data yield identification of possible scattering mechanisms for each area of interest. It was found that backscatter from the ocean is highly polarized and well-modeled by Bragg scattering, while scattering from trees in a city park possesses a considerable unpolarized component. Urban regions exhibit the characteristics expected from dihedral corner reflectors and their polarization signatures are quite different from the one-bounce Bragg model.
311 citations
TL;DR: In this paper, the problem of light scattering by a sphere on a substrate is treated using Mie's solution for scattering a sphere in a homogeneous medium and an extension of Weyl's method for the calculation of the reflection of dipole radiation by a flat surface.
Abstract: The problem of light scattering by a sphere on a substrate is treated using Mie's solution for scattering by a sphere in a homogeneous medium and an extension of Weyl's method for the calculation of the reflection of dipole radiation by a flat surface. The developed theory can be applied to spheres with a radius of the order of the wavelength of the incident light. Particular solutions are given for the case of a perfectly conducting substrate and for the so-called static limit. In the latter case it is shown that the solution is equivalent to that obtained by Wind, Vlieger and Bedeaux for small spheres.
290 citations
TL;DR: A theoretical modeling is proposed to predict the efficiency factors for attenuation, total scattering, and backscattering for spherical and homogeneous phytoplanktonic cells in suspension to evaluate the reliability of the model for algal cells of various indices and morphologies.
Abstract: A theoretical modeling is proposed to predict the efficiency factors for attenuation, total scattering, and backscattering for spherical and homogeneous phytoplanktonic cells in suspension. The input parameters of this modeling are the actual size distribution, the spectral values of absorption by the living cells, and an adjustable value of the real part of the refractive index. The variations in these parameters lead to very diverse spectral behavior of the efficiency factors. Theoretical predictions are compared to experimental results for some species to evaluate the reliability of the model for algal cells of various indices and morphologies.
274 citations
262 citations
TL;DR: In this paper, a simple dynamic scaling law was found on the scattering function I(q,t), where q is the scattering vector and ξ(t)=q−1m(t) is the correlation length of the periodic unmixed structure at time t which is measured by the position qm (t) of the scattering maximum at time T. The universal scaling functions (or the scaled structure function) F[qξ (t)] experimentally determined from the scattering functions for the lower quench depths (i.e., unmixing at 96.8
Abstract: Unmixing kinetics of quenched critical polymer mixture of polystyrene and poly(vinyl methyl ether) was investigated by time‐resolved light scattering technique. In the late stage of spinodal decomposition τ>60, τ being a reduced time, a simple dynamic scaling law was found on the scattering function I(q,t); I(q,t)∼ξ(t)3S[qξ(t)] with ξ(t)∼ta, where q is the scattering vector and ξ(t)=q−1m(t) is the correlation length of the periodic unmixed structure at time t which is measured by the position qm(t) of the scattering maximum at time t. The universal scaling functions (or the scaled structure function) F[qξ(t)] experimentally determined from the scattering functions for the lower quench depths (i.e., unmixing at 96.8, 97.3, and 98.2 °C, the spinodal temperature Ts being 95.8 °C) are in good agreement with that predicted by Furukawa, S(x)∼x2/(3+x8) for the critical mixtures (percolation regimes) in three dimensions [x=qξ(t)], although the scaling functions F(x) experimentally determined for the higher quen...
TL;DR: In this paper, a light-scattering technique for measuring the diameter of transparent droplets is described, based on the theory of ray optics, which is done on-line by a microcomputer.
01 Feb 1986
TL;DR: In this paper, the structure and interactions in aqueous dispersions of a synthetic hectorite-type clay, Laponite RD, have been investigated at low ionic strength ([Na] ∼ 10−3 mole dm−3) by static (SLS) and dynamic light scattering (DLS), and small angle neutron scattering (SANS).
Abstract: The structure and interactions in aqueous dispersions of a synthetic hectorite-type clay, Laponite RD, have been investigated at low ionic strength ([Na] ∼ 10−3 mole dm−3) by static (SLS) and dynamic light scattering (DLS) and small angle neutron scattering (SANS). At low concentrations (≲0.01 g ml−1) both SLS and DLS show that the dispersions contain discrete particles, which do not interact strongly. The molecular weight and hydrodynamic properties of these particles are similar to those of circular disks of diameter ∼30 nm and thickness ∼ 1 nm. At higher concentrations (≳0.03 g ml−1), where gelation and the development of elasticity occurs, there are clear indications of interparticle interactions from changes in the light scattering and SANS behavior. These interactions are ascribed to an overlap of the electrical double layers surrounding the clay particles. It is proposed that the resultant interparticle repulsion gives rise to an equilibrium structure, having elastic properties, in which the translational mobility of the particles is restricted. From the scattering behavior there is no evidence of an association of the particles in an edge-to-face type structure which is now accepted to occur extensively at much higher ionic strengths in other clay dispersions, such as kaolinites and bentonites. The proposed gelation mechanism of Laponite dispersions at low ionic strength is, however, likely to be similar to that which has been suggested previously from rheological studies to occur with montmorillonite, which is a clay which can also undergo osmotic swelling.
Book•
18 Aug 1986
TL;DR: One-Magnon Light Scattering from Ferromagnets and Ferrimagnets as discussed by the authors is a classic example of light-scattering from pure antiferromagnetic detectors.
Abstract: Basic Theory. Experimental Methods. One-Magnon Light Scattering From Ferromagnets and Ferrimagnets. One-Magnon Light Scattering From Pure Antiferromagnets. Two-Magnon Light Scattering From Pure Antiferromagnets. Light Scattering From Impure Magnets. Light Scattering at Magnetic Surfaces. Concluding Remarks. References. Subject Index. Chemical Formula Index.
TL;DR: In this article, the authors measured the absolute phase of the surface second-harmonic light field with respect to the pump field, i.e. the phase of surface nonlinear susceptibility.
TL;DR: In this article, it was shown that if the grains in composite media are large enough to give rise to magnetic dipole and higher-order multipole radiation, then the effective permeability of the composite medium cannot be taken to be that of free space even if the gra...
Abstract: Effective-medium theories yield effective dielectric functions (or, equivalently, refractive indices) of composite media. Such theories have been formulated that go beyond the Maxwell-Garnett and Bruggeman theories, which art restricted to media composed of grains much smaller than the wavelength. These extended effective-medium theories do not, however, yield effective dielectric functions that can be used for the same purposes for which we unhesitatingly use the dielectric functions of substances such as pure water and pure ice (e.g., reflection and transmission by smooth interfaces; absorption and scattering by particles). Extended dielectric functions can lead to unphysical results; for example, absorption in composite media with nonabsorbing components. Moreover, if the grains in composite media are large enough to give rise to magnetic dipole and higher-order multipole radiation, then the effective permeability of the composite medium cannot be taken to be that of free space even if the gra...
TL;DR: The measurements of the reflectance of sand wetted with various liquids are in reasonably good agreement with the simple theory and it is suggested that the difference between reflectances of wet and dry surfaces may have implications for remote sensing.
Abstract: It is commonly observed that natural multiple-scattering media such as sand and soils become noticeably darker when wet. The primary reason for this is that changing the medium surrounding the particles from air to water decreases their relative refractive index, hence increases the average degree of forwardness of scattering as determined by the asymmetry parameter (mean cosine of the scattering angle). As a consequence, incident photons have to be scattered more times before reemerging from the medium and are, therefore, exposed to a greater probability of being absorbed. A simple theory incorporating this idea yields results that are in reasonable agreement with the few measurements available in the literature, although there are differences. Our measurements of the reflectance of sand wetted with various liquids are in reasonably good agreement with the simple theory. We suggest that the difference between reflectances of wet and dry surfaces may have implications for remote sensing.
TL;DR: In this article, a simple model in which anisotropic scattering is considered by means of transformed parameters w' and r' was proposed to estimate the scattering and absorption properties of the canopy.
Abstract: Microwave radiation from a canopy cover depends primarily on the vegetation's thermal and dielectric properties; the latter are dependent on plant biometrical parameters and water content. Emission measurements carried out by means of ground-based X-and Ka-band radiometers have shown that crop coverage of soil can be detected through the spectral signatures of bare soil and vegetation. Moreover, measured brightness temperature and the radiative transfer theory for a scattering medium allow estimation of the scattering and absorption properties of the canopy. These parameters have been computed for corn and alfalfa using experimental data and a simple model in which anisotropic scattering is considered by means of transformed parameters w' and r'. We found that the single scattering albedo w' is always lower than 0.1, whereas the optical depth T' is very high. The latter has been correlated to plant water content by means of a logarithmic function.
TL;DR: In this article, the positions between the plane-parallel electrodes were probed by pulsed laser light scattering at several wavelengths and the particle nucleation and growth kinetics were very well demonstrated over this range of discharge parameters.
Abstract: We report laser diagnostic studies of capacitively coupled RF discharges containing 0.05-0.45-percent silane in argon. We probed positions between the plane-parallel electrodes by pulsed laser light scattering at several wavelengths. These spatial scans had a resolution of 0.25 mm and they showed unusual particle distributions which varied with silane mole fraction and gas-flow rates. Particle nucleation and growth kinetics were very well demonstrated over this range of discharge parameters. We also studied particle photophysics and demonstrated that ultraviolet pulsed lasers (251.4 and 266 nm) can form silicon atoms from laser-particle interactions. Atoms were formed in both ground and excited states with a concentration that depended linearly on laser energy. However, atoms were not formed by 354- or 532-nm excitation. Particle excitation by 354 nm at energies > 0.5 mJ created a long-time (>0.1 s) perturbation of the discharge chemistry which linearly increased the steady-state (10 Hz) light scattering with increasing 354-nm energy.
TL;DR: In this article, the amplitudes for specular reflection and refraction at the surface of an isotropic, intrinsically nonmagnetic chiral medium are derived for sets of constitutive relations that are invariant or non-invariant under a duality transformation of the electromagnetic fields.
Abstract: Fresnel amplitudes for specular reflection and refraction at the surface of an isotropic, intrinsically nonmagnetic chiral medium are derived for sets of constitutive relations that are invariant or noninvariant under a duality transformation of the electromagnetic fields. The invariant set leads to a differential reflection curve of incident left and right circularly polarized light that is null at normal incidence and peaks beyond Brewster’s angle; the noninvariant set leads to maximum differential reflection in the vicinity of normal incidence and extends over a wide range of incident angles. Both sets lead to effectively equivalent descriptions of standard optical rotation and circular dichroism.
TL;DR: The angular line shape of the scattered light in an infinite medium and the reflected light from a half-space and a slab is found and is different from that found for scalar waves.
Abstract: The scattering of light from a disordered medium is considered. The effects of polarization and the transverse nature of the light on the coherent backscattering arising from weak localization phenomena are calculated. The angular line shape of the scattered light in an infinite medium and the reflected light from a half-space and a slab is found. The scattered light contains several components and the line shape is different from that found for scalar waves. The results are in qualitative agreement with recent experiments.
TL;DR: Mise en evidence experimentale des effets de la localisation faible dans la diffusion de the lumiere, par des mesures de retrodiffusion coherente sur un diffuseur constitue de microparticules de BaSO 4.
Abstract: We report the first observation of weak localizations effects in light scattering by a disordered solid. For a diffuse solid scatterer we predict and observe (i) multiple backscattering speckle, (ii) a coherent backscattered peak remaining after removal of this speckle by ensemble averaging, and (iii) speckle statistics which differ from those for single scattering. Computer simulations based upon the theoretical equations yield results in good agreement with experiment.
TL;DR: In this article, the effects of non-Lambertian reflection from a homogeneous surface on remote sensing of the surface reflectance and vegetation index from a satellite were discussed.
Abstract: This paper discusses the effects of non-Lambertian reflection from a homogeneous surface on remote sensing of the surface reflectance and vegetation index from a satellite. Remote measurement of the surface characteristics is perturbed by atmospheric scattering of sun light. This scattering tends to smooth the angular dependence of non-Lambertian surface reflectances, an effect that is not present in the case of Lambertian surfaces. This effect is calculated to test the validity of a Lambertian assumption used in remote sensing. For the three types of vegetations considered in this study, the assumption of Lambertian surface can be used satisfactorily in the derivation of surface reflectance from remotely measured radiance for a view angle outside the backscattering region. Within the backscattering region, however, the use of the assumption can result in a considerable error in the derived surface reflectance. Accuracy also deteriorates with increasing solar zenith angle. The angular distribution of the surface reflectance derived from remote measurements is smoother than that at the surface. The effect of surface non-Lambertianity on remote sensing of vegetation index is very weak. Since the effect is similar in the visible and near infrared part of the solar spectrum for the vegetations treated in this study, it is canceled in deriving the vegetation index. The effect of the diffuse skylight on surface reflectance measurements at ground level is also discussed.
TL;DR: It is shown that nonsphericity always increases Qabs for size parameters larger than ∼10, while it decreases g—and correspondingly increases β—in the size range 8 ≤ x ≤ 15, and Concavity almost always enhances the spherical–nonspherical differences.
Abstract: Using the extended boundary condition method, scattering calculations from randomly oriented rotationally symmetric nonspherical particles were made, the size parameters (1-25) and the refractive indicies (1.5 0.02i) of which were chosen to relate to the transfer of solar and IR radiation in an aerosol atmosphere. Comparison of computations for 23 Chebyshev shapes to corresponding size-averaged spherical results revealed that nonsphericity increased absorption for size parameters larger than around 10 and decreased the asymmetry factor, and correspondingly increased the backscattered fraction, in the size ranges 8-15. The scattering efficiency was somewhat larger for nonspherical particles, while the single-scattering albedo tended to be smaller, and concavity was shown to almost always enhance spherical-nonspherical differences.
TL;DR: In this paper, small angle neutron scattering (SANS) is used to investigate the local order in aqueous, charge stabilized suspensions of 103 A diameter polystyrene latexspheres at ∼14 wt.
Abstract: Small angle neutron scattering(SANS) is used to investigate the local order in aqueous, charge stabilized suspensions of 103 A diameter polystyrene latexspheres at ∼14 wt. % solids. These samples which evidence a close packed close packed structure in equilibrium are observed to undergo a transition to an amorphous order when sustaining a sufficiently large and steady shear. The shear melting phenomonology is different from that observed by light scattering for very dilute (0.16 wt. % solids) suspensions of polystyrene particles which form bcc lattices in equilibrium. Furthermore, neutron scattering reveals more detail than light scattering for concentrated suspensions and indicates a larger degree of three‐dimensional ordering under steady shear flow than is implied by sliding layer models for similar systems.
TL;DR: A localized approximation to the generalized Lorenz-Mie theory is introduced based on van de Hulst’s localization principle and validation is obtained from numerical comparisons the Rayleigh-Gans theory.
Abstract: Relying on van de Hulst’s localization principle, a localized approximation to the generalized Lorenz-Mie theory is introduced. The validation of this simple approximation is obtained from numerical comparisons the Rayleigh-Gans theory. Other comparisons concerning scattering profiles are carried out first with theoretical data published in the literature and later with experimental measurements. Original results are given for coal particles as an example of the versatility of the method.
TL;DR: The maximum entropy method (MEM) is used to analyze quasielastic light scattering correlation functions as discussed by the authors, and the success of the method is illustrated with results from computer generated noisy data and experimental data from colloidal dispersions.
Abstract: The maximum entropy method (MEM) is used to analyze quasielastic light scattering correlation functions. The central problem, in such data analysis, is the recovery of the distribution of exponentials describing the decay of the correlation function (i.e., inverting the Laplace transform). MEM is shown to give a high‐quality reconstruction of these distributions. The success of the method is illustrated with results from computer‐generated ‘‘noisy’’ data and with experimental data from colloidal dispersions. Both the theoretical properties, and practical advantages of MEM are presented and compared with current data analysis techniques.
TL;DR: In this article, a large number of experimental methods have been developed, but they are often limited in their applicabilities, such as emission, adsorption, or scattering of massive particles; only a few rely on optical probing.
Abstract: Surface probing and characterization play an essential role in the progress of surface science and technology (1) . For this purpose, a large number of experimental methods have been developed, but they are often limited in their applicabilities. New surface probes are always in great demand. Among the existing techniques (1) , many involve emission, adsorption, or scattering of massive particles; only a few rely on optical probing. The optical methods have, in general, the advantages of being nondestructive, capable of in-situ remote sensing with high spatial and tc mporal resolution, and applicable to any interface accessible by light. The difficulty of these methods oft en lies in the lack of surface specificity and sensitivity. Linear optical absorption and reflection, for example, can be employed for sur face studies only if the dominant bulk contribution to the signal can be discriminated against (2) . The same is true with light scattering. Recent advances in lasers and optical detection systems have led to the invention of several novel surface tools. Laser-induced desorption (3) , photo acoust ic spectroscopy (4) , and photothermal deflection spectroscopy (5) have been developed for spectroscopic studies of adsorbates and sur face states. Resonance fluorescence (6) and multiphoton ionization (7) have been used to measure energy redistribution in molecules scattered or desorbed from a surface. V arious surface nonlinear optical effects have also been seriously considered for surface studies. Stimulated Raman gain
TL;DR: In this paper, aqueuses de salicylate d'alkyl-trimethylammonium and of palmitylpyridinium have been found.
Abstract: Resultats de l'etude des solutions aqueuses de salicylate d'alkyl-trimethylammonium et de salicylate de palmitylpyridinium